How do you solve this?

Test Preparation SAT Preparation
1

<p>If x^2=y^2+20 and x-y=4, find the value of x+y.</p>

<p>A) 16
B) 10
C) 8
D) 5
E) 4</p>

2

<p>Rearrange the first equation to:</p>

<p>X^2-y^2=20
(x-y)(x+y)=20
4 (x+y) = 20
X+y = 5</p>

3

<p>Set x-y=4 equal to x (x=y+4)</p>

<p>Substitute x in x^2=y^2+20</p>

<p>(y=4)^2=y^2+20</p>

<p>Solve for y</p>

<p>y = 1/2</p>

<p>Replace y in x-y=4</p>

<p>x = 9/2</p>

<p>x+y (9/2+1/2)</p>

<p>=5</p>

<p>Answer is D</p>